The long-range objectives of this Learning Disabilities Research Center are the identification, characterization, validation, and amelioration of etiologically distinct subtypes or dimensions of learning disabilities. To accomplish these objectives, test batteries that include measures of cognitive abilities (Research Project I), reading and language processes (Research Project II), and ADHD and executive functions (Research Project III) will be administered to a unique sample of 50 pairs of identical twins and 50 pairs of fraternal twins in which at least one member of each pair has a significant difficulty in the acquisition and use of mathematics, to an independent sample of 50 pairs of identical twins and 50 pairs of fraternal twins in which at least one member of each pair is reading disabled, and to a comparison group of 50 pairs of identical twins and 50 pairs of fraternal twins with a school history of no significant difficulty in mathematics or reading. Resulting data will be used to assess the genetic and environmental etiologies of deficits in mathematics and reading, as well as their covariation with measures of phonological and orthographic coding, ADHD, and executive functions. In order to search for major genes and/or quantitative trait loci that may influence learning disabilities, blood samples will be drawn from fraternal twin pairs and subjected to genetic linkage analyses (Research Project IV). Concurrently, a sample of 100 twin pairs will be administered differential computer-based remediation to assess possible subtype-by-treatment interactions (Research Project V). An administrative core unit will be responsible for coordinating the activities of the five research projects; maintaining communication among the participating investigators; ascertaining and scheduling subjects; obtaining questionnaire data from families of twins; compiling and managing i a master file of combined data sets; and administering the Center budget and other fiscal matters.